This invention relates to writing apparatus, and more particularly to an improved ink drop writing apparatus which controls a writing fluid in response to an input signal so as to directly record certain input information on a writing medium.
FIG. 1 is a schematic drawing of a presently known arrangement which will be described to provide an understanding of the type of device to which this invention is directed. A nozzle 1 is vibrated by an electromechanical transducer 3, which is connected to a high frequency power source 2. The transducer 3 is usually placed adjacent to or around the nozzle 1. Ink 4 is fed to the nozzle 1 under pressure in the direction of an arrow A causing an ink stream 5 to be emitted from the nozzle with a predetermined velocity. The ink stream 5, which is produced by the nozzle 1, is subjected to periodic constrictions as a result of the vibration of the nozzle. The constrictions grow as the ink stream travels so that ink drops 6 are regularly generated from the stream in synchronism with the high frequency vibration.
At this time, a signal voltage from a recording pattern signal-generator source 8, which is synchronized in frequency with the excitation of the electromechanical transducer 3 and whose amplitude corresponds to a recording information input B, is applied to a charging electrode 7, for charging the ink drop, with a predetermined phase corresponding to the drop generating phase. The ink drop 6 is thereby charged in response to the applied signal voltage. Thereafter, the ink drop is deflected according to the charge thereon corresponding to the recording pattern signal voltage by an electrostatic field which is established by deflecting electrodes 9, across which a d.c. high voltage source 10 is connected.
The ink drops unnecessary for forming a recording pattern receive no charge and are not deflected by the deflecting electrodes 9. Thus, these ink drops proceed along a linear path and are intercepted by a waste catcher 11, and only the necessary drops which have a charge thereon are deflected to pass above the waste catcher and form recording dots on a writing medium or paper 12. While the ink drops are being deflected and scanned in a Y-direction on the basis of the above principle for deflecting the ink drops, the nozzle 1 and the paper 12 are relatively moved in an X-direction. As a result, a stripe-like recording pattern 13 can be obtained.
In such an ink drop writing apparatus, the distance or amount of deflection D of the ink drop in the Y-direction can be expressed by the following well known relationship (refer to FIG. 2); ##EQU1## where M : mass of the ink drop,
Q : amount of charge on the ink drop, PA1 V.sub.d : flying velocity of the ink drop, PA1 E : strength of the deflecting electrostatic field, PA1 b : extent of the deflecting electrostatic field in the flying direction of the drop, PA1 L : distance between the end of the deflecting electrostatic field and the paper. As apparent from the principle of the writing operation, the amount of deflection D of the ink drop is directly related to the width of the pattern to be recorded on the paper and the recording position. In FIG. 2, numeral 14 designates the deflecting electrostatic field. Unless the amount of deflection of the ink drop for a given charge in the drop is held constant, the width and the position of the pattern will change, and a proper recording pattern 13A, as indicated in FIG. 3, will become distorted, as shown at 13B or 13C. Accordingly, where the recording pattern 13 is composed of characters, the magnitude and the line space of the characters change.
Where the recording is reproduced by successively arraying stripe-like recording patterns, as described, a proper arrayal, as shown at (1) in FIG. 4, becomes a distorted pattern as shown at (2) in which an interstice appears and the patterns are doubled. Where the stripe-like recording patterns are recorded in superposition, for example where recording dots by ink drops of different colors are formed for color indication, undesirable misregistration of the patterns and color shading take place.
Among the variables in the equation (1), E, b and L can be set at relatively precise predetermined values comparatively easily. These can be kept substantially constant without any problem in practical use as against changes in the surroundings of the writing apparatus even in the case of operation of the apparatus over a long period of time. In contrast, the values of M, Q and V.sub.d are difficult to set at precise predetermined values and to be held constant at these values against the changes in the surroundings and in case of the operation of the apparatus over a long period of time. Thus, when efforts are made to hold these variables at the required predetermined values in order to avoid the inconveniences stated previously, the ink drop writing apparatus is prone to become very complicated.
For example, the temperature of the ink is liable to rise due to a change in the ambient temperature of the ink drop writing apparatus or because of the running of the apparatus for a long period of time. For this reason, the properties (such as surface tension and viscosity) of the ink will change, or the pressure for supplying the ink to the nozzle will change. In consequence, the flying velocity V.sub.d of the ink drop or the mass M thereof changes, so that the amount of deflection D of a drop of given charge in a predetermined electrostatic field changes. Further, since the length of the ink stream changes with a rise in the temperature of the ink, the degree of coupling between the ink stream and the charging electrode changes. Therefore, the amount of charge Q changes, and the deflection distance D changes in turn. In order to avoid the changes in the amount of deflection D, complicated means are required for keeping the temperature and properties of the ink constant as well as means for supplying the ink under constant pressure to the nozzle.